Reference may be made to the following patents of interest: Italian Pat. No. 410185; and U.S. Pat. Nos. 3,995,962; 3,789,562; 4,313,687; 4,353,662; 4,355,918; 3,632,147; 3,876,316; 3,980,408; 3,982,841; 4,027,449; 4,131,380; 4,193,706; 4,162,860; 4,371,279.
Currently available space frame and space truss systems include a plurality of structural elements, such as hollow tubes, arrayed in a geometric pattern, with the ends of the tubes connected together at joints or nodes by connecting members. A variety of connecting members are available cooperating with the tube end structure and the nodes for structurally interconnecting the joint elements.
In one such commercial unit, hollow tubular structural members are connected to the nodes by bolts slidably mounted in the tube ends and held from falling into the tube by a spanner sleeve pinned to the bolt. While this arrangement has been found relatively satisfactory in use, it is relatively expensive to manufacture because spanner sleeves or nuts with slots are utilized. Also, this structure requires an erection hole to be provided near the tube end so that prying pressure can be applied to the bolt head to aid in engaging the threads into the node. Thus, all structural members in such a system must be hollow. Furthermore, if the bolt threads are damaged significantly in shipping or handling, the entire member may have to be replaced, thereby increasing the cost of the system.
In other commercial systems, the nodes are hollow and access holes are provided to allow for tightening of the connecting bolts or nuts from inside the node. This type of system typically requires larger nodes with some type of removable cap on the node. The larger node size can be aesthetically displeasing, and the removable caps can provide an access point for undesired moisture to enter into the node. Tightening of the bolts or nuts from inside the node is often difficult and may require special tools. Also, in order to achieve the structural design capacity of compression members, extremely precise and consistent member lengths must be maintained. In addition, attachment of members or other items may be difficult or impossible to accomplish at the removable cap locations. The structural integrity of hollow nodes is also a concern which must be taken into account when designing and manufacturing these components.
Various other types of structural members are represented in the above-mentioned patents. Many of the above-mentioned patents illustrate a connecting member between the node and a structural rod in the space frame system wherein the connecting member is captured such as by an end cap or nut in either the node or the rod and may threadably engage the other member, as shown in U.S. Pat. Nos. 4,313,687; 4,353,662; 4,355,918 and others.
Certain of the patents illustrate a connecting member which threadably engages a node at one end and a structural rod member at the other end. For example, U.S. Pat. No. 3,995,962 employs a threaded bolt with different pitch threads on opposite bolt ends so that the bolt threadably engages the node faster than the bolt is threadably disengaged from the rod during assembly. In U.S. Pat. No. 3,789,562, a threaded node and threaded strut member are interconnected by a threaded bolt which threadably engages the node. A short plug or bushing has inner and outer threads with the inner threads engaging the bolt and the outer threads engaging the strut. In Italian Pat. No. 410185, one embodiment contains a threaded node and threaded rod with a threaded bolt threadably engaging both the node and the rod. A pair of nuts are threadably engaged on the bolt and are used to lock the assembly in position.
These aforementioned patents as well as the prior recited commercial units require a multiplicity of parts, some of which are of special construction and therefore expensive to manufacture. In many cases, such prior art units cannot be conveniently shipped without the possibility of losing many of the small components which requires a stockpile of extra components at the erection site, or delays the eventual erection of the space frame system. In other instances, such prior art units are inordinately complex and require special tools to assemble and are therefore expensive and time consuming.
Accordingly, it is desired to provide improved structural joint members for a space framework system in which the components are relatively simple and therefore inexpensive to manufacture, contain a minimum number of individual components and wherein the structural joint is as small as possible without sacrificing structural integrity. It is also desired to provide such components which can be pre-assembled for shipping while reducing component loss and which can be relatively easily assembled at the erection site.